Classical T Tauri star accretion activity and variability can also be studied by using veiling. This is the filling-in of stellar photospheric absorption features such that they appear shallower in observed spectra of an actively accreting young star, due to an accretion-fueled flux excess (both in the continuum and in lines). This phenomenon has been investigated since [1]} first introduced the concept of veiling. With high resolution spectroscopy, it is possible to observe the photospheric absorption lines of the star and this excess due to accretion that effectively veils the spectrum.
